Pressures, Tempatures, Amperages

[54regcab]

Is there a site/page that explains how pressures and temperatures affect compressor amperage? If the indoor coil is warmer (pressure up) does the compressor amperage increase or decrease?

[Shophound]

Compressor amps increase with a load increase. Higher indoor air temps will impose a higher load on the evaporator coil. Higher outdoor air temperatures reduce the effectiveness of the condenser to reject heat, which increases compressor head pressure.

If a system is overcharged, it will also increase compressor amp draw over where it should be with a proper charge under similar weather conditions. Same applies if the outdoor coil is dirty, or if there is return air duct leakage, such as a leaking return in an attic.

[54regcab]

So the more pressure difference between low and high side increases compressor amperage? Wouldn't a warmer evap coil decrease the temp difference between inside and out? Or is it when overall pressure on both sides increases that compressor amps increase?

[beenthere]

Only Pro members with an * beside their name may answer questions in the AOP forums.

[Shophound]

So the more pressure difference between low and high side increases compressor amperage? Wouldn't a warmer evap coil decrease the temp difference between inside and out? Or is it when overall pressure on both sides increases that compressor amps increase?

My "*" designation is pending (beenthere, I have asked ice, who in turn has run it up the flagpole) so I hope my reply can remain for the moment. If it is deleted I understand.

To answer your question, 54, the greater a difference there is between suction and discharge pressures, the more work the compressor must do. It is also less efficient, especially a reciprocating compressor, since it cannot expel all of the refrigerant from its cylinders before it intakes more. We in the trade refer to this difference in pressures as compression ratio, and seasoned pros know that the higher the compression ratio is, the less efficient the pump is, and the more power it will draw to accomplish work.

[beenthere]

My "*" designation is pending (beenthere, I have asked ice, who in turn has run it up the flagpole) so I hope my reply can remain for the moment. If it is deleted I understand.

To answer your question, 54, the greater a difference there is between suction and discharge pressures, the more work the compressor must do. It is also less efficient, especially a reciprocating compressor, since it cannot expel all of the refrigerant from its cylinders before it intakes more. We in the trade refer to this difference in pressures as compression ratio, and seasoned pros know that the higher the compression ratio is, the less efficient the pump is, and the more power it will draw to accomplish work.

Your post will remain unless Admin says other wise.

[54regcab]

So it's like a regular air compressor that you can actually hear "loading up" as it builds pressure? BTW when did the new policy that only pro members can answer questions go into effect? I've received some good advice over the past 10 years from people that don't have the "pro" designation.

[beenthere]

Its Pro members with an * beside their name. regular guest also may not answer questions/give advise.

Went into effect today.

[Shophound]

So it's like a regular air compressor that you can actually hear "loading up" as it builds pressure?

Good analogy. An ammeter on an air compressor motor filling its tank would show an increase in current draw as the air pressure continued building in the tank.

You've stumbled upon what many OEMs of a/c units already know. As part of their quest to meet higher SEER constraints, they play with compression ratios on the compressor. This is done by larger condenser coils, larger evaporators, and slightly undersized compressors.

[heaterman]

So it's like a regular air compressor that you can actually hear "loading up" as it builds pressure? BTW when did the new policy that only pro members can answer questions go into effect? I've received some good advice over the past 10 years from people that don't have the "pro" designation.

The "rules of engagement" as it were have been changed. The site is leaning toward guiding the general posting public with more in-depth answers to their questions. In an attempt to prevent wrong or misleading technical answers from getting some homeowners in trouble and or danger, vetting professionals with the "*" after their professional member moniker was instituted to make it easier to keep track.